Method of connecting individual conducting layers of a nanolaminate structure

ABSTRACT

Nanolaminate materials are composed of alternating layers of two materials, such as conducting and insulating materials, that are synthesized by sputter coating on a flat substrate with a large number of layers. By employing lithographic processing during the deposition process, it is possible to make separate electrical contact to specific subsets of the metallic layers in the composite nanolaminate. Any number of separate electrodes is possible, in principle. This allows for multiple electrochemical circuits for simultaneous cyclic voltammetry in a single detection electrophoretic channel. The improvement allows for electrophoretic flow of 1 electrolyte and the electrochemical detection and discrimination of various analyte particles. The microfluidic component can be incorporated in a device for the purpose of analyzing or performing a chemical or biological assay on a very small fluid electrolyte, such as water. Such devices can be used as pathogen detectors.

[0001] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to sensors utilizing nanolaminates, particularly to nanolaminate components having electrodes deposited on the metal layers of the nanolaminate, and more particularly to the forming of nanolaminate structures with separate electrical contact formed during the deposition of the nanolaminate structure.

[0003] The ability to collect and organize atoms, molecules, nanocrystals, colloids, cells, proteins and spores on a substrate is a major goal of nanoscience and technology and has enormous potential in the fields of material science, synthetic chemistry, biology and medicine, as well as national security. There has been a problem in developing a technology in which the structural scale of a template can be engineered by man to match the scale of a nanobody and thereby manipulate it to form an ordered structure or to selectively absorb the nano body enabling assay and analysis. This has been addressed using standard lithographic approaches in the past that cannot, at this time, achieve nano dimensions over significant areas in the range less than 70 nm.

[0004] Recently nanolaminate structures have been developed for sensors wherein a polished surface of the structure is exposed to a sample fluid passing thereacross. Such an approach is described and claimed U.S. application Ser. No. 10/167,926 filed Jun. 11, 2002. Also, sensor utilizing separated nanolaminate structures, each having a polished surface exposed to a sample fluid have been developed, with this approach being described and claimed in U.S. application Ser. No. 10/(IL-10906), filed ______, 2002.

[0005] The present invention involves the addition of separate electric contacts formed in the nanolaminates during deposition. Electrical contact with individual metal nanolaminate layers permits their use as an electrode in the fluid channel. The sequence of metallic layers is envisioned as being periodic, so that the pattern of connection repeats. This is accomplished by employing lithographic processing during the deposition of the nanolaminate materials, such as by magnetron sputtering. By this invention, it is possible to make separate electric contacts with any two or more groups of metallic or conducting layers of the nanolaminates.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to enable interconnection of selected conductive layers of a nanolaminate.

[0007] A further object of the invention is to provide a method for connecting individual conducting layers of a nanolaminate structure.

[0008] It is a further object of the invention to connect conducting layers of a nanolaminate structure by employing lithographic processing.

[0009] Another object of the invention is to provide a method employing lithographic processing during the deposition process to form separate electrical contacts to specific subsets of the metallic layers in the nanolaminate composite.

[0010] Another object of the invention is to connect individual conducting layers of a nanolaminate structure thereby enabling multiple electrochemical circuits for simultaneous cyclic voltammetry in a single nanolaminate electrophoretic channel.

[0011] Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves a method for connecting individual conducting layers of a nanolaminate structure. By employing lithographic processing during the deposition process, wherein nanolaminate materials composed of alternating layers of two materials (typically conducting and insulating layers) that are synthesized (deposited) by sputter coating a flat substrate with a large number of layers, separate electrical contacts can be made to specific subsets of the metallic layers of the nanostructure. Thus, electrical contact can be made with every conducting layer, every other conducting layer, every third conducting layers, every second and fourth conducting layers, etc. Interconnection of any number of separate (individual) electrodes is possible. This allows for multiple electrochemical circuits for simultaneous cyclic voltammetry in a single nanolaminate electrophoretic channel. This improvement allows for electrophoretic flow of electrolyte and the electrochemical detection and discrimination of various analyte particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings which are incorporated into and form a part of the disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0013]FIG. 1 is a view of an embodiment of a nanolaminate structure with a central section removed to form a fluid flow channel therethrough.

[0014]FIG. 2 illustrates schematically illustrates a nanolaminate having alternating layers of conductive and insulative layers, with the conductive layers electrically connected to an electrical contact.

[0015]FIG. 3 schematically illustrates a separated pair of nanolaminate structures with interdigitated electrode electrically connected to electrical contacts.

[0016]FIG. 4 is a schematic plot of the electrical potential along the edge of the fluid channel of a device as in FIG. 3.

[0017]FIG. 5 schematically illustrates an embodiment involving four sets of interdigitated electrodes.

[0018]FIG. 6 is a schematic plot of the voltage profile of the FIG. 5 device, near the nanolaminate surface along the electrophoretic channel.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention is directed to connecting individual conducting layers of a nanolaminate structure. The conducting layers may be connected via a variety of patterns, such as all layers connected, every other layer, every third layer, every second and fourth layers, etc. so as to enable any number of conductive layers to be interconnected. A periodic sequence useful but is not required. This invention also enables the formation of interdigitated electrodes from two or more nanolaminate electrodes.

[0020] Nanolaminate materials are composed of alternating layers of two materials (typically conducting and insulating layers) that are synthesized by sputter coating a flat substrate with a large number of (i.e., multiple) layer pairs. By employing lithographic processing during the deposition process, it is possible to make separate electrical contacts to specific subsets of the metallic (conducting) layers in a composite. Any number of separate electrodes is possible, in principle. This allows for multiple electrochemical circuits for simultaneous cyclic voltammetry in a single nanolaminate electrophoretic channel. This invention allows for electrophoretic flow of electrolyte and the electrochemical detection and discrimination of various analyte particles.

[0021] By way of example, the method of the invention, if carried out in its simplest form would involve depositing a layer of insulator on a substrate, then depositing a layer of metal on the insulator layer, patterning the metal layer using lithographic processing so that when the next layer of insulator was deposited, a void would be formed in one end, thereafter depositing another layer of metal over the insulator layer, through the void and onto the metal layer below, thereby forming an electrical contact between the two metal layers via the void in the intermediate insulator layer. FIGS. 2, 3 and 5 illustrate the method being carried out to form interdigitated electrode or electrical conducting members electrically connected to selected metallic layers of the nanolaminate structure, this being done using lithographic processing during deposition of the nanolaminate structures.

[0022] Sputter deposition of nanolaminate structures or composites creates nearly uniform coatings of material over large areas. Patterning the metallic layers of these structures has been suggested as a way to form capacitors with nanometer-scale-separation of metallic layers. This interdigitation places distinct metal layers at particular surfaces of the composite. The separate electrodes may be used to perform both electrophoretic pumping and cyclic voltammetry. This is a single-nanolaminate version of an earlier design, see above referenced copending applications, of an electrophoretic/electrochemical channel composed of two separate nanolaminates. This version does not require physical juxtaposition and alignment of two separate nanolaminates. It is envisioned that the opposite electrodes will be held at potential differences on the order of volts, so as to effect electrochemical redox reactions. The breakdown voltage for nanolaminates is of the order of 4 MV/cm. Therefore, nanolaminates with electrode separations on the order of 100 nm can support voltage differences of 4 volts. It is not required that the separate, interdigitated electrodes be in close proximity; other patterns of interleaving are possible.

[0023] Referring now to FIG. 1, an embodiment of a nanolaminate is illustrated generally at 10 with interdigitated metal layers 11 separated by insulating layers 12. Alternate metallic layers 11 terminate on the left and right sides of nanolaminate 10, allowing separate electrical contact to the interleaved layers. An electrophoretic fluid channel indicated by arrow 13 has been established through a center section of the nanolaminate. As shown in FIG. 2, a separate resistive film 14 is placed in good electrical contact with the sides of the nanolaminate, only one side shown, and metallic layers 11 are connected electrically thereto, as indicated at 15. This permits the formation of an adjustable voltage difference between successive layers in the composite or nanolaminate. Electrical currents may be passed through the resistive films 14 in the vertical direction, so that at the same time there is a quasi-uniform change in potential along the length of the channel 13.

[0024]FIG. 3 is a schematic view of a two component nanolaminate of the single component as shown in FIG. 1, and showing the added resistive films 14, the metallic layers or electrodes 11, and labeling the electric potentials required to drive electrophoretic flow (V) and simultaneous electrochemical I (V′) measurements. FIG. 4 is a schematic plot of the electrical potential along the edge of the fluid channel such as seen at 13 in FIG. 1 near the metallic electrodes (solid line), and near the center of the channel 13 that is wider than the electrolyte Debye length (dotted line). The peak-to-peak variation is V′, while the (exaggerated) average slope is V/w for the applied voltage across the entire channel length, equal to the nanolaminate dimension, w.

[0025] It is useful to generalize this concept for improved detection and discrimination of particles in a detector. Rather than simple binary interdigitation, it is possible to deposit the stacked metallic layers with extensions that conceptually resemble the staggered tabs in a stack of manila folders (with numerous variations possible). The exposed stacks of one set of metallic layers would be well-separated from the adjacent stacks for other metallic layers so that independent electrical contacts can be established. Electrodes at the fluid channel can then be given multiple voltages. For example, denoting the electrode layers as 1-4, the voltage pattern at the fluid channel need not be . . . V₁V₂V₁V₂ . . . , but can repeat with . . . V₁V₂V₃V₄ . . . (or even be nonrepetitive), see FIGS. 5 and 6.

[0026] Electrode 1 can be back-etched to a depth D₁, (i.e., it can be separately electrochemically etched), have a width W₁, or set of widths {W₁} (determined by the sputter deposition sequence), and relative voltage of V₁. Electrode 2 would have parameters D₂W₂ and V₂ etc. Spacings between the successive electrodes, W₁₂,W₂₃, etc. can also be varied at will by controlling the nanolaminate deposition sequence. Because the periodic electrode pattern repeats over large distances, every electrode 1 is equivalent, excepting only the ends of the channel. (This is true even if there is a steady voltage drop along the channel to drive electrophoretic flow at the same time that electrochemical detection is attempted.) The different voltages, sizes, spacings, etc. of electrodes will lead to a different electrochemical current through each of the electrodes pairs, depending on size, oxidation/reduction potentials, mobility, charge, etc. Differences may be used to distinguish types of analytes by principal component or linear discriminant analysis, or other techniques.

[0027] For carrying out the above example, four (4) layer-interleaved nanolaminate is envisioned, with the layers viewed slightly offset from the deposition surface, thereby showing the various metallic layers with “tabs”, or separable electrical contact points. Four distinct metal layers would be provided.

[0028]FIG. 5 illustrates a schematic plot of a portion of the resulting envisioned electrochemical circuit for the four separate sets of electrodes, the separate sets being indicated at 1, 2, 3 and 4 (any numbers of electrodes are possible).

[0029]FIG. 6 is a schematic plot of the voltage profile near the nanolaminate surface along the electrophoretic channel of the FIG. 5 arrangement. The four separate regions around the multiply-interdigitated electrodes are depicted in the plot as regions 1-4. The sequence is understood to repeat many times. Four separate, simultaneous I(V) measurements between electrode pairs are possible: 1-2, 1-4, 3-2, and 3-4. This includes parallel charge transport between any electrode labeled 1 and the nearest electrode 2, second nearest electrode 2, etc.

[0030] It has thus been shown that the present invention enables connecting individual conducting layers of a nanolaminate structure. This is accomplished employing lithographic processing during the deposition process of the nanolaminate.

[0031] It is possible using this method to make separate electrical contacts to specific subsets of the metallic layers in the nanolaminate. Any number of separate electrode is possible.

[0032] While particular embodiments of the invention have been described to exemplify and teach the principles of the invention, such are not intended to be limiting. Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only the scope of the appended claims. 

What is claimed is:
 1. In a method for fabricating nanolaminate structures having conducting and insulating layers, the improvement comprising: forming an electrical contact with at least one conducting layer during or after deposition of the conducting and insulating layers.
 2. The improvement of claim 1, wherein the forming of the electrical contact is carried out utilizing lithographic processing.
 3. The improvement of claim 1, wherein the forming of the electrical contact is carried out to form a separate electrical contact with specific subsets of the conducting layers of the nanolaminate.
 4. The improvement of claim 1, wherein forming of the electrical contact is carried out by: depositing a layer of conducting material, patterning at least an area of the layer of conducting material, depositing a layer of insulating material on the layer of conducting material except in the patterned area so as to define a void in the layer of insulating material, and depositing a layer of conducting material on the layer of insulating material and in the void thereby producing an electric contact between the layers of conducting material.
 5. The improvement of claim 1, additional including forming a number of electrical contacts with conducting layers of the nanolaminate structure to produce at least one interdigitated electrode.
 6. The improvement of claim 6, additionally including providing a plurality of interdigitated electrodes on a plurality of nanolaminate structures.
 7. A nanolaminate structure, comprising: a number of conducting layers, a number of insulating layers, said conductive layers being intermediate adjacent insulating layers, and at least one separate electric contact operatively connected to at least one of said conducting layers.
 8. The nanolaminate structure of claim 7, wherein said electric contact is operatively connected to a number of said conductive layers.
 9. The nanolaminate structure of claim 7, additionally including a number of electric contacts operatively connected to a number of conducting layers.
 10. The nanolaminate structure of claim 7, wherein said electric contact is of an interdigitated configuration.
 11. The nanolaminate structure of claim 7, including a number of electrical conducting means defining a plurality of interdigitated electrodes.
 12. A method for connecting individual conducting layers of a nanolaminated structure, comprising: forming alternating layers of conducting and insulating layers, and during deposition of the conducting and insulating layer forming at least one electric contact layer so as to be in electrical contact with at least one conducting layer.
 13. The method of claim 12, wherein forming at least one electric contact layer, is carried out utilizing lithographic processing. 